I've never noticed a post sunrise peak nor any sunset peak, post or
otherwise, but I certainly have experienced sunrise peaks and can confirm
that they exist.
Sunrise peaks don't always happen and when they do, they usually enhance
the signal only slightly. On occasion they can be quite conspicuous. I
remember one time when a ZS was S9+30 db on 160m SSB at his sunrise. I
have worked VKs on 160m SSB starting at S9 about 15 minutes before local
sunrise and continuing the QSO through my sunrise when the VKs would peak
at S9+30 db. Then the signals would rapidly drop off to nil immediately
after my sunrise. These conspicuous peaks are rare.
Perhaps the reason that a sunrise peak sometimes enhances signals only
slightly is that it is not really a peak at all, but a drop in ambient
noise level at one's sunrise time. This may be because noise is no
longer propagated in from the east at sunrise and weak signals from the
west can be more easily heard. If there is a sunset peak, it may be for
the same reason in the opposite direction.
I have always used low-angle vertical polarization, but those with
high-angle horizontal antennas may have different observations.
73, de Earl, K6SE
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